Most helicopters incorporate an empennage-mounted tail rotor system to counteract the torque effects produced by the main rotor system. Proper operation of the tail rotor system is necessary for safe and efficient helicopter flight operations, especially in the hover flight mode.
The tail rotor system is driven by power diverted from the helicopter powerplant, such power being transmitted to the tail rotor system by means of a tail rotor drivetrain. The tail rotor drivetrain includes a primary tail rotor driveshaft that extends between the powerplant and an empennage torque-coupling device, e.g., intermediate gear box, tail rotor gear box, and which is operative to facilitate power transfer to the tail rotor system. The primary tail rotor driveshaft is typically housed within the helicopter boom structure. Due to the length of most primary tail rotor driveshafts, such shafts are rotatably supported within the boom structure by one or more support bearing assemblies, e.g., hangar bearings, duplex bearings.
Such support bearing assemblies represent crucial operating components of the drivetrain that directly affect the proper operation of the tail rotor system. Mechanical degradation of the support bearing assemblies due to bearing defects has a direct negative impact on the operating performance of the tail rotor system. Moreover, such bearing defects, as well as excessive bearing operating temperatures, may lead to catastrophic failure of the affected support bearing assemblies, which, in turn, results in the operational loss of the tail rotor system. Excessive bearing operating temperatures may result from a number of diverse causes, such as inadequate maintenance, e.g., contaminated lubricant, degraded lubricant, inadequate quantity of lubricant, or excessive quantity of lubricant, improperly manufactured bearings, e.g., inadequate retainer to ball clearance, inadequate retainer to race clearance, or inadequate internal clearance, and excessive bearing loads, e.g., improper driveshaft system component assembly (misalignment; out of balance condition), or damaged driveshaft system components (bent; out of balance condition).
Monitoring the health of support bearing assemblies is a paramount concern for safe and efficient helicopter operations. Prior art techniques for monitoring helicopter support bearing assemblies have generally been limited to periodic physical inspections of the respective drivetrain components. Periodic inspections, however, are not necessarily reflective of the actual operating condition of the support bearing assemblies. Furthermore, such static inspections are generally conducted without the benefit of standardized inspection criteria, relying to an unnecessary degree upon the individual skills of maintenance personnel. In consequence, rapid or very slow rates of degradation may not be effectively identified during such periodic inspections.
These physical inspections have been supplemented by the temporary installation of measuring equipment to monitor the operating condition of selected components such as the support bearing assemblies. Utilizing temporarily installed measuring equipment for periodic inspections, however, requires degradation rates greater than the measurement period to be effective such that the utility of such equipment is limited.
A need exists for a bearing assembly monitoring system that provides real time, continuous monitoring of the operating condition of support bearing assemblies, especially support bearing assemblies that comprise helicopter tail rotor drivetrains. The system should be operative to provide real time warnings of bearing degradation and/or impending catastrophic failure. The system should be operative to effectively eliminate false alarms. The system should utilize operating condition parameters that may be readily correlated and standardized to indicate bearing degradation and/or impending catastrophic failure of specific support bearing assemblies.